A plastic optical material is used in the production of various lenses, prisms, optical disc substrates and the like because of its transparency, light weight, and excellent molding properties. As such plastic materials, transparent resins such as polymethyl methacrylate, polycarbonate and the like are mainly used (JP-A-56-131654 and JP-A-58-1261119). The term "JP-A" as used herein means an "unexamined published Japanese patent application".
Such plastic optical materials, however, are required to have excellent optical properties such as the balance between a refractive index and a dispersion value, photoelastic constant and the like as well as properties such as transparency, heat resistance, low water absorption properties, mechanical strength, surface hardness and the like. Polymethyl methacrylate has disadvantages that its heat resistance is low and its water absorption is large. The conventional polycarbonate derived from bisphenol A has disadvantages that its photoelastic constant is large, melt fluidity is relatively poor and as a result, a the birefrigence of a molded article increases.